In one class of fuel injectors, a reciprocating plunger is utilized to pressurize fuel to initiate and sustain injection. With each reciprocation, pressure gradients along the plunger can oscillate between zero and about 20,000 psi or more at a frequency of many times per second. Because of this high cyclic pressure gradient, fuel naturally has the tendency to leak past the plunger along the plunger bore wall. For a number of reasons, including decreased complexity, increased reliability, allowable fuel leakage, concerns about where and how to route the leaked fuel and for other reasons known to those skilled in the art, it is often desirable to eliminate leakage past the plunger by using an O-ring seal. However, because of the high frequencies involved in injection cycles and the extreme magnitude of cyclic pressure changes acting on an O-ring seal, most presently available O-rings tend to fail long before the other components of the fuel injector. In other words, O-ring technology has not sufficiently advanced to provide reliable and long term sealing at the high frequencies and relatively extreme pressures experienced within a fuel injector environment.
The present invention is directed to overcoming this and other problems associated with sealing against fluid leakage past a reciprocating cylindrical member within a fuel injector.